We have found out that the Custodial Parent of my step children is smoking Marijuana, is there anything I can do? I have emails from her when I confronted her about it, and she never denied the usage of using the drugs. Any suggestions would be great.

Thanks

IF you can prove it is having an adverse effect on the children,
IF she is smoking it in the same room with them or involving them in any way
Then you need to document everything you can and take it to children's protective services. Most often they won't do anything about parents for smoking marijuana because too many do.